1. Field of the Invention
The present invention relates to a sampling filter and radio communication apparatus, and more particularly to a sampling filter and radio communication apparatus that perform frequency conversion, filter processing, and so forth, by means of analog processing.
2. Description of the Related Art
In a mobile communication or suchlike radio communication apparatus, a sampling filter apparatus is used that temporally discretizes a signal and performs frequency conversion and filtering. An example of a conventional sampling filter apparatus is that shown in Unexamined Japanese Patent Publication No. 2004-289793 (page 16, FIG. 3b). FIG. 1 shows the conventional sampling filter apparatus presented in Patent Document 1.
As shown in FIG. 1, conventional sampling filter apparatus 10 has transconductance amplifier 20 and sampling circuit 30. This sampling circuit 30 has history capacitor 32, sampling capacitors 34 and 36, and switch 38. Sampling capacitors 34 and 36 are banks of rotation capacitors 42, and also have switches 44 and 46.
Transconductance amplifier 20 supplies a radio frequency (RF) current to sampling circuit 30. The RF current is integrated by history capacitor 32—that is, a charge is accumulated on history capacitor 32. The RF current flow to history capacitor 32 is controlled by switch 38. Switch 38 is controlled by a signal generated by a digital control unit (DCU).
RF current is also supplied to rotation capacitor 42. When switch 44 is turned on a charge is accumulated on rotation capacitor 42, and when switch 46 is turned on an already accumulated charge is read. Switch 44 and switch 46 are also controlled by a signal generated by a digital control unit (DCU).
With a conventional sampling filter having this kind of configuration, a discrete time sample stream can be created by cyclically reading charges accumulated in rotation capacitors 42.